Inner qualities of continuous casting billet/slab such as crack and porosity are mainly affected by distribution and intensity of the secondary cooling water, the surface temperature of billet/slab during the continuous casting process is an important feedback parameter in the secondary cooling water control. However, it is hard to measure the surface temperature of billet/slab because of iron scale producing randomly on it and abominable measuring conditions such as high temperature and tense steam, etc. This technique problem has not been well tackled yet, and this is the main reason for not realizing closed-loop control of secondary cooling water in continuous casting.
A Chinese patent with the Publication Number CN1410189 discloses a kind of “Method for Accurately Measuring the Casting Billet Surface Temperature in the Secondary Cooling Zone of Continuous Casting”, in which several infrared radiation thermometer are employed to measure the temperatures of many fixed points on the surface of casting billet/slab, and the maximum value obtained from these temperature measurement points within every 30 seconds to 2 minutes is chosen as the accurate temperature value of the surface of casting billet/slab. The shortcomings of the mentioned method lies: in the first place, for the reason that the iron scale on the surface of the casting billet arises randomly, the maximum temperature values measured during different sampling periods even at the same point vary significantly, that is, the influence of the iron scale is not overcome well so that the measured temperature value is unstable; in the second place, the sampling period of 30 seconds to 2 minutes has a long lag time, thus real-time feedback and control of the secondary cooling water cannot be realized.
Due to the strong oxidizing environment and the strong water cooling operation in continuous casting, the iron scales with uneven thicknesses and unpredictable location that are randomly generated on the surface of the casting billet/slab are different from those evenly distributed on the surface of steel slab in the metallurgical reheating furnace or in the steel rolling process. The radiation-based temperature measurement for the casting billet/slab surface is greatly affected by the existence of the uneven iron scales. The aforementioned prior art cannot overcome the influence of the iron scale on the temperature measurement of the surface of casting billet/slab, so that the surface temperature of billet/slab cannot be measured accurately and stably. Hence, there is still a need for a temperature measuring method and apparatus for measuring the surface temperature of continuous casting billet/slab, which is able to overcome the influence of the iron scale on the surface of casting billet/slab.